I think what is confusing me is that I don't know what you mean by "the spektrum tx modules I have already" and "make them think they are pluged into a JR R-1 JRPRO module slot", especially when you say later "I just dont have the actual radio"
An Arduino cannot receive or send wireless data without being connected to some sort of wireless module.
And in your Original Post you said "I have a twin engine nitro rc car and I want a rpm and temp readers on each engine" which leads me to think that you want to send data by wireless from your car to your base unit. AFAIK standard R/C equipment just sends data from the base unit to the car.
I know how to send data in both directions, but not with Spektrum equipment. However if you can explain more clearly what you are trying to do I may be able to help.
The reason I mentioned the Deltang modules is because they use Cypress wireless devices and are compatible with Spektrum R/C transmitters. I was not trying to encourage you to take up railway modelling.
...R